The present invention relates to the formation of semiconductor devices. More specifically, the present invention relates to etching process for dielectric layers.
During semiconductor wafer processing, features of the semiconductor device are defined in the wafer using well-known patterning and etching processes. In these processes (photolithography), a photoresist (PR) material is deposited on the wafer and then is exposed to light filtered by a reticle. The reticle is generally a glass plate that is patterned with exemplary feature geometries that block light from propagating through the reticle.
After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the photoresist material such that a developer can remove a portion of the photoresist material. In the case of positive photoresist materials, the exposed regions are removed, and in the case of negative photoresist materials, the unexposed regions are removed. Thereafter, the wafer is etched to remove the underlying material from the areas that are no longer protected by the photoresist material, and thereby define the desired features in the wafer.
Argon-fluoride (ArF) excimer laser having wavelength of 193 nm (ArF lithography technology) has been used to for the production of sub 0.04 μm devices. This immersion lithography technology enables processes below the 110 nm node. Such small features in most highly integrated circuits require higher resolution and thus a thinner photoresist because of the depth-of-focus (depth-of-field) limitations of the patterning image. For example, the ArF lithography for certain DRAM processes, such as Bitline, uses a very thin photoresist with a thickness less than 100 nm. The photoresist material is also softer and weak, and such a thin photoresist would easily and undesirably be etched during a plasma etching process for one or more antireflective coating (ARC) layers, such as the bottom antireflective coating (BARC) and silicon oxynitride (SiON) layers, after patterning of the photoresist. Thus, it has been one of the major challenges in the short-wavelength lithography to manage the “etch budget” and prevent surface degradation of the photoresist, while achieving target critical dimensions (CD). Here, “etch budget” is typically the amount of time during which an exposed structure (the photoresist in this case) can be subjected to etchant without undue damages.
In addition, an ideal etching process must accurately transfer the pattern on the mask to an underlying layer to be etched. However, since the etching process removes a target material both chemically and physically, the etching process is very sensitive to various environmental parameters. One of such factors in conventional etching control is the micro-loading effect, in which the characteristics of the etching differ under the variation of size and density of the pattern (feature), i.e., the variation of the “loading”, of a layer to be etched (an etch layer).